¹Zhichen Zhao (>10)
Journal of Geophysical Research: Planets (in Press), Link to Article [DOI: 10.1029/2026JE009684]
¹MOE Key Laboratory of Advanced Micro‐Structured Materials, Shanghai Frontiers Science Center of Digital Optics, Institute of Precision Optical Engineering, and School of Physics Science and Engineering, Tongji University, Shanghai, China
Published by arrangement with John Wiley & Sons

Nanophase iron (np-Fe0$$), as one of the key products of space weathering, is widely observed in the near-surface layer of lunar materials, providing crucial evidence for their geological evolution. Here we report the discovery of np-Fe0$$ with a rare lamellar morphology, embedded in Fe-Ti-Cr oxide solid solutions within the interior of the lunar meteorite NWA 4734, characterized by nanometer-scale thicknesses and micrometer-scale lateral dimensions. Notably, these lamellae exhibit a unique three-layer core-shell structure, consisting of np-Fe0$$ core, Fe3+$$-bearing shell, and ilmenite-dominated outer layer. This finding offers new insights into the formation process of np-Fe0$$ in lunar materials through thermal decomposition and disproportionation associated with impact events and space weathering, and reveals a novel pathway for nanomaterial synthesis under extreme conditions.

^1,2N. Imae
Journal of Geophysical Research: Planets, 131, e2026JE009763 Open Access Link to Article [DOI: 10.1029/2026JE009763]
¹National Institute of Polar Research (NIPR), Tokyo, Japan
²The Graduate University for Advanced Studies (SOKEDAI), Tokyo, Japan
Published by arrangement with John Wiley & Sons

Enstatite chondrites record highly reducing conditions in the early solar nebula, yet the origin of their abundant sulfides remains unclear. Niningerite (MgS) and oldhamite (CaS) are ubiquitous in EH3 enstatite chondrites and distinguish them from other chondrite groups. To investigate sulfide formation, we conducted sulfidation experiments under ultra-reducing conditions using evacuated silica-glass tubes to reproduce extremely low oxygen pressure environments. Experiments at 1,200–1,420°C and IW−5 to −6 with pyrrhotite–troilite buffers examined reactions of Mg- and Ca-bearing silicates with sulfur-rich gas. Niningerite formed from forsterite–enstatite, and oldhamite from diopside, producing granular niningerite surrounding olivine and enstatite and granular oldhamite associated with diopside, coexisting with cristobalite and enstatite. Mg–Fe compositions of synthetic niningerite are included in those in EH3 chondrites. In the experiments, niningerite and oldhamite did not form within the coexisting Fe-S reservoir, whereas natural EH3 meteorites show enrichment of these sulfides in metal-sulfide nodules, a key discrepancy with natural EH3 textures. This suggests that the precursors of chondrules and metal nodules—aggregates of chondrules and metal nodules—underwent melting and segregation events, during which niningerite and oldhamite preferentially partitioned into the metal nodules. These multi-stage high-temperature processes provide new constraints on the physicochemical environment of sulfide formation in the inner solar nebula.